Lathe

ABSTRACT

A chuck operating apparatus includes a claw, a shifter, and a shifter drive unit. The rotatable claw has a first posture to bring the chuck into the opened state and a second posture to bring the chuck into the closed state. The rotatable shifter is brought in a first position to bring the claw into the first posture and in a second position to bring the claw into the second posture. The shifter drive unit has a shifter lever having an insertion part provided with a shifter bearing capable of being brought into contact with a side surface of an outward groove of the shifter. A roller is provided on one of the claw and the shifter in a contact position with the other to roll in a spindle axis direction and a groove is formed on the other to receive the roller when the chuck is in the opened state.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of PCT Application No.PCT/JP2019/042480, filed on Oct. 30, 2019, which claims priority ofJapanese Patent Application No. 2018-235842 filed on Dec. 17, 2018. Thecontents of this application are incorporated herein by reference intheir entirety.

BACKGROUND (a) Field

The present invention relates to a lathe provided with a spindle havinga chuck capable of releasably holding a workpiece.

(b) Description of the Related Art

In a well-known NC (numerical control) lathe, a front side of aworkpiece held by a front spindle is machined and the workpiece is thenpassed to a back spindle for back machining to be performed on a backside of the workpiece. The front spindle and the back spindle each has achuck such as a collet to hold the workpiece. As disclosed in JapanesePatent Application Publication No. 2018-149643 (especially, FIG. 2), thechucking mechanism has a shifter and a tilt claw. The shifter is mountedoutside the spindle and movable in the spindle axis direction. The clawhas an end protruding forwards to be in contact with the outercircumference of the shifter. The claw tilts in a direction that thedistance between the end and the spindle axis varies. The shifter is ofa shape surrounding the spindle on the spindle axis. A plurality ofclaws are in contact with the shifter. The shifter and the claws rotateon the spindle axis. The shifter moves to the rear to tilt the claw in adirection that the end separates from the spindle axis. The collet isthereby closed by a sleeve to hold the workpiece. The shifter moves tothe front to tilt the claw in a direction that the end approaches thespindle axis by force of a collet open spring. The collet is therebyopened to release the workpiece.

A shifter drive unit has a shifter lever to move the shifter in thespindle axis direction. An outward groove is entirely formed around anouter surface of the shifter with respect to the spindle axis to receivean insertion part of the shifter lever. The shifter rotates on thespindle axis. The shifter lever does not rorate on the spindle axis. Theinsertion part of the shifter lever is provided with a shifter bearing.A shifter bearing of coaxial type has an inner ring rotatable on thespindle axis to fit in the outward groove of the shifter. The coaxialshifter bearing is larger in diameter since it is mounted outside theshifter with respect to the spindle axis. A shifter bearing of oppositetype has an outer ring rotatable on a rotation axis perpendicular to thespindle axis to be capable of being brought into contact with a frontside surface or a rear side surface of the outward groove. The oppositeshifter bearing is smaller and less expensive than the coaxial shifterbearing.

Technical Problem

The shifter and the claw are in contact with each other. They rubagainst each other by operation of the chuck. Repeated machining causeswear of the shifter and the claw. A roller is provided in a contactposition of the shifter and the claw to roll in the spindle axisdirection. If a shifter bearing is kept in contact with the side surfaceof the outward groove of the shifter, the shifter bearing easily wearsdue to produced heat since a smaller bearing rotates faster than theback spindle. It is therefore desired that the shifter bearing isseparated from both the side surfaces of the outward groove when theinsertion part of the shifter is not activated. When the collet isclosed, the shifter pushes the end of the claw in a diameter directionperpendicular to the spindle axis. The shifter is thereby kept not tomove in the spindle axis direction to keep the shifter bearing separatedfrom both the side surfaces of the outward groove. When the collet isopened, however, the shifter is released from such force to bring theshifter bearing into contact with the front side surface or the rearside surface of the outward groove. That shortens the life of theshifter bearing.

The present invention discloses a lathe capable of elongating the lifeof the shifter bearing.

A lathe of the invention includes a spindle rotatable on a spindle axisand provided with a chuck having a closed state to hold a workpiece andan opened state to release the workpiece and a chuck operating apparatuswhich opens and closes the chuck. The chuck operating apparatus includesa tilt claw provided outside the spindle and rotatable on the spindleaxis, the claw having a first posture to bring the chuck into the openedstate and a second posture to bring the chuck into the closed state; ashifter provided outside the spindle and rotatable on the spindle axis,the shifter being movable in a direction of the spindle axis to bebrought in a first position to bring the claw into the first posture andin a second position to bring the claw into the second posture; and ashifter drive unit having a shifter lever which moves the shifter in thedirection of the spindle axis. An outward groove is entirely formedaround an outer surface of the shifter with respect to the spindle axisto receive an insertion part of the shifter lever. The insertion part ofthe shifter lever has a shifter bearing capable of being brought intocontact with a side surface of the outward groove. A roller is providedon one of the claw and the shifter in a contact position with the otherto roll in the direction of the spindle axis and a groove is formed onthe other to receive the roller when the chuck is in the opened state.

The invention provides a lathe capable of elongating the life of theshifter bearing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a configuration of a lathe.

FIG. 2 is a vertical section view schematically showing a sub headstock.

FIG. 3 is a perspective view around a chucking mechanism.

FIG. 4 is a vertical section view around the chucking mechanism.

FIG. 5 is a perspective view of a claw.

FIG. 6 is a perspective view of a claw holder.

FIG. 7 is a perspective view of a shifter.

FIG. 8 schematically shows a shifter drive unit.

FIG. 9 is a vertical section view of the chucking mechanism in the statethat a chuck is opened.

FIG. 10 is a vertical section view of the chucking mechanism when theshifter reaches a second position to close the chuck.

FIG. 11 is a vertical section view of the chucking mechanism in thestate that an insertion part of a shifter lever is separated from bothside surfaces of an outward groove when the shifter is in the secondposition.

FIG. 12 is a vertical section view of the chucking mechanism when theshifter reaches a first position to open the chuck.

FIG. 13 is a vertical section view of the chucking mechanism ofouter-claw type provided with a shifter having a roller in the statethat the chuck is closed.

FIG. 14 is a vertical section view of the chucking mechanism ofouter-claw type provided with a shifter having a roller in the statethat the chuck is opened.

FIG. 15 is a vertical section view of the chucking mechanism ofinner-claw type provided with a claw having a roller in the state thatthe chuck is closed.

FIG. 16 is a vertical section view of the chucking mechanism ofinner-claw type provided with a claw having a roller in the state thatthe chuck is opened.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be described.The invention is not limited to the exemplary embodiment and thefeatures disclosed herein are not necessarily essential to theinvention.

(1) Technology Included in the Invention:

Technology of the invention will be described with reference to FIG. 1to FIG. 16. The drawings only schematically show an example of theinvention. They may have a mismatch to each other due to differentmagnification in each direction. Each element denoted by a symbol isonly an example.

Embodiment 1

A lathe 1 of an embodiment of the technology may include a spindle (aback spindle 52, for example), a spindle support 53, a built-in motor55, and a chuck operating apparatus 6. The spindle (52) rotatable on aspindle axis AX0 may be provided with a chuck 60 mounted at the frontend thereof. The chuck 60 may have a closed state ST2 to hold aworkpiece W0 and an opened state ST1 to release the workpiece W0. Thespindle support 53 may rotatably support the spindle (52) by a frontbearing B1 and a rear bearing B2. The built-in motor 55 may be disposedbetween the front bearing B1 and the rear bearing B2 to drive thespindle (52). The chuck operating apparatus 6 may include a tilt claw 20and a shifter 10 to open and close the chuck 60. The claw 20 may bemounted outside the spindle (52) and between the front bearing B1 andthe rear bearing B2. The claw 20 may have a first posture PO1 to bringthe chuck 60 into the opened state ST1 and a second posture PO2 to bringthe chuck 60 into the closed state ST2. The claw 20 may have a movableend 21 whose distance from the spindle axis AX0 varies between the firstposture PO1 and the second posture PO2. The shifter 10 may be mountedoutside the claw 20 and movable in a direction of the spindle axis AX0(a Z-axis direction, for example). The shifter 10 may be brought in afirst position LO1 to bring the claw 20 into the first posture PO1 andin a second position LO2 to bring the claw 20 into the second posturePO2.

A comparative chucking mechanism of outer-claw type is being explainedreferring to FIG. 13 and FIG. 14. A chucking mechanism 6 b having theshifter 10 and the claw 20 may be disposed in a position on the rearside of the rear bearing. The shifter 10 may be mounted outside the backspindle 52 and movable in the Z-axis direction. The claw 20 may protrudeforwards to keep contact with the outer circumference of the shifter 10and have the movable end 21 tilting in a direction that the distancefrom the spindle axis AX0 varies. The shifter 10 may be of a shapesurrounding the back spindle 52 with respect to the spindle axis AX0. Aplurality of the claws 20 may be in contact with the shifter 10. Theshifter 10 and the claw 20 may rotate on the spindle axis AX0. As shownin FIG. 14, the claw 20 may further have an extended heavier portion 22c provided on the rear side of a tilt axis to prevent the movable end 21from going away from the spindle axis AX0 due to centrifugal forcegenerated by forward movement of the shifter 10. The shifter 10 may beextended forwards from around the front end of the claw 20.

The chucking mechanism of outer-claw type is longitudinal in the spindleaxis direction. It is therefore difficult to simply dispose such longermechanism between the front bearing and the back bearing where thebuilt-in motor is mounted. An additional intermediate bearing would berequired to rotatably support the high speed rotation spindle. Sucharrangement would make the headstock structure complicated and elongatethe front part of the spindle too long. Further, the chucking mechanismdisposed in a position on the rear side of the rear bearing would bedisadvantageous to high speed rotations of the spindle.

In a chucking mechanism 6 a according to Embodiment 1 of the invention,the shifter 10 may be mounted outside the claw 20 that is mountedoutside the spindle 52. The shifter 10 may be movable in the directionof the spindle axis AX0. The chucking mechanism 6 a may be shorter thanthe chucking mechanism 6 b in the spindle axis direction, thereforeeliminating the need of an intermediate bearing even when both thechucking mechanism 6 a and the built-in motor 55 are disposed betweenthe front bearing B1 and the rear bearing B2. The front part of thespindle (52) may be necessarily elongated to avoid interference of theheadstock (51) with another structure such as a tool post 30. Then thechucking mechanism 6 a may be disposed in a space of the headstock (51)supporting the elongated front part of the spindle (52). A rear part ofthe spindle (52) may be shortened instead. The emodiment provides alathe capable of shortening the spindle in the spindle axis direction.

The spindle may include a main spindle also referred to as a frontspindle and a sub spindle also referred to as a back spindle. The chuckmay include a collet, a claw, and a variety of holders capable ofholding a workpiece. The workpiece may include a product conceptually.The remarks described above may be applied to the following embodiments.

Embodiment 2

The lathe 1 may include a main headstock (a front headstock 41, forexample) provided with a main spindle (a front spindle 42, for example)holding the workpiece W0, a tool post 30 machining the workpiece W0 heldby the main spindle (42), and a sub headstock (a back headstock 51, forexample) provided with a sub spindle (the back spindle 52, for example)opposite the main spindle (42) and receiving the workpiece W0 from themain spindle (42). The sub spindle (52) may correspond to the spindle inEmbodiment 1. The sub headstock (51) moving in the spindle axisdirection has a risk of interference with the tool post 30 machining theworkpiece W0 held by the main spindle (42). The front part of the subspindle (52) may be elongated to avoid such interference. The chuckingmechanism 6 a may be then disposed in an elongated front space of thesub headstock (51) adapted to the elongated front part of the subspindle (52) and the rear part of the sub spindle (52) may be shortenedinstead. The embodiment provides a lathe capable of shortening the subspindle in the spindle axis direction.

Embodiment 3

The claw 20 and the shifter 10 may be mounted in a position on the frontside of the built-in motor 55 with respect to the direction of thespindle axis AX0. The chucking mechanism 6 a may be smaller in diameteron the spindle axis AX0 while the built-in motor 55 may be larger. It istherefore convenient to arrange the chucking mechanism 6 a in theelongated front space of the headstock (51) adapted to the elongatedfront part of the spindle (52) to avoid interference of the headstock(51) with the tool post 30 and other structures. The chucking mechanism6 a disposed in the elongated front space may be closer to the chuck 60mounted at the front end of the spindle (52), which simplifies thestructure of the chuck operating apparatus 6. The embodiment provides alathe capable of shortening the spindle in the spindle axis direction.

Embodiment 4

The lathe 1 of another embodiment of the invention may include thespindle (the back spindle 52, for example) and the chuck operatingapparatus 6. The spindle (52) may be rotatable on the spindle axis AX0and provided with the chuck 60 having the closed state ST2 to hold theworkpiece W0 and the opened state ST1 to release the workpiece W0. Thechuck operating apparatus 6 may include the claw 20 and the shifter 10to open and close the chuck 60. The tilt claw 20 mounted outside thespindle (52) may have the first posture PO1 to bring the chuck 60 intothe opened state ST1 and the second posture PO2 to bring the chuck 60into the closed state ST2. The shifter 10 mounted outside the spindle(52) may be movable in the direction of the spindle axis AX0 to bebrought in the first position LO1 to bring the claw 20 into the firstposture PO1 and in the second position LO2 to bring the claw 20 into thesecond posture PO2. The shifter 10 may be provided with a roller 15 in acontact position with the claw 20. The roller 15 may roll in thedirection of the spindle axis AX0.

The roller 15 may be attached to the shifter 10 in the contact positionwith the claw 20. The roller 15 may roll in the spindle axis directionwhen the chuck 60 is operated. The friction of the shifter 10 againstthe claw 20 is reduced and the load on a driving source of the shifter10 is thereby reduced. The roller 15 and the claw 20 touching each othergradually wear but wear amount is reduced. The embodiment facilitatesparts replacement since replacement of the roller 15 does not require atime-consuming replacement of the whole shifter 10 mounted entirelyaround the spindle (52). The roller may be attached to the claw 20. It,however, would gradually cause wear of the roller and the shiftertouching each other and result in replacement of the whole shifter. Inthis embodiment, only the roller is the contact point of the shifter andthe claw, which eliminates the need of replacement of the whole shifter.The embodiment provides a lathe capable of facilitating maintenance ofthe chucking mechanism.

Embodiment 5

The shifter 10 may be provided with a hold 14 removably having a pin (aroller pin 16, for example) extended along a rolling axis AX3 of theroller 15. The roller 15 may have an insertion hole 15 a through whichthe pin (16) is passed in the AX3-axis direction. The roller 15 may rollon the pin (16) passed in the hole 15 a. An operator can take the roller15 out of the shifter 10 only by removing the pin (16) from the hold 14.The operator can attach the roller 15 to the shifter 10 only by mountingthe pin (16) passed in the hole 15 a to the hold 14. The embodimentprovides a lathe capable of facilitating maintenance of the chuckingmechanism.

Embodiment 6

The lathe 1 of another embodiment of the invention may include thespindle (the back spindle 52, for example) and the chuck operatingapparatus 6. The spindle (52) may be rotatable on the spindle axis AX0and provided with the chuck 60 having the closed state ST2 to hold theworkpiece W0 and the opened state ST1 to release the workpiece W0. Thechuck operating apparatus 6 may include the claw 20, the shifter 10, anda shifter drive unit DR1 to open and close the chuck 60. The tilt claw20 mounted outside the spindle (52) may have the first posture PO1 tobring the chuck 60 into the opened state ST1 and the second posture PO2to bring the chuck 60 into the closed state ST2. The shifter 10 mountedoutside the spindle (52) may be movable in the the spindle axisdirection to be brought in the first position LO1 to bring the claw 20into the first posture PO1 and in the second position LO2 to bring theclaw 20 into the second posture PO2. The shifter drive unit DR1 may havea shifter lever 68 to move the shifter 10 in the direction of thespindle axis AX0. The shifter 10 may have an outward groove 12 formedentirely around an outer surface 11 of the shifter 10 with respect tothe spindle axis AX0 to receive an insertion part 68 a of the shifterlever 68. The insertion part 68 a may be provided with a shifter bearingB3 capable of being brought into contact with a side surface 12 a, 12 bof the outward groove 12. The roller 15 rolling in the direction of thespindle axis AX0 may be provided in one of the claw 20 and the shifter10 in a contact position with the other. A groove 25 may be formed onthe other to receive the roller 15 when the chuck 60 is in the openedstate ST1.

When the chuck 60 is in the opened state ST1, the roller 15 mounted onone of the claw 20 and the shifter 10 may fit in the groove 25 formed inthe other. Accordingly, the shifter bearing B3 can be kept separatedfrom both the side surfaces 12 a and 12 b of the outward groove 12 ofthe shifter 10 even when the chuck 60 is in the opened state ST1. Theembodiment provides a lathe capable of elongating the life of theshifter bearing.

Embodiment 7

The lathe 1 of another embodiment of the invention may include thespindle (the back spindle 52, for example) and the chuck operatingapparatus 6. The spindle (52) may be rotatable on the spindle axis AX0and provided with the chuck 60 having the closed state ST2 to hold theworkpiece W0 and the opened state ST1 to release the workpiece W0. Thechuck operating apparatus 6 may include the claw 20, the shifter 10, andthe shifter drive unit DR1 to open and close the chuck 60. The tilt claw20 mounted outside the spindle (52) and rotatable on the spindle axisAX0 may have the first posture PO1 to bring the chuck 60 into the openedstate ST1 and the second posture PO2 to bring the chuck 60 into theclosed state ST2. The shifter 10 mounted outside the spindle (52) androtatable on the spindle axis AX0 may be movable in the direction of thespindle axis AX0 (the Z-axis direction, for example) to be brought inthe first position LO1 to bring the claw 20 into the first posture PO1and in the second position LO2 to bring the claw 20 into the secondposture PO2. The shifter drive unit DR1 may have the shifter lever 68 tomove the shifter 10 in the direction of the spindle axis AX0. Theshifter 10 may have the outward groove 12 formed entirely around theouter surface 11 thereof with respect to the spindle axis AX0 to receivethe insertion part 68 a of the shifter lever 68. The insertion part 68 amay be provided with the shifter bearing B3 capable of being broughtinto contact with the side surface 12 a, 12 b of the outward groove 12.The shifter drive unit DR1 may drive the shifter lever 68 to first movethe shifter 10 in the direction of the spindle axis AX0 and thenseparate the shifter bearing B3 from the side surface 12 a, 12 b of theoutward groove 12.

The shifter lever 68 driven by the shifter drive unit DR1 may first movethe shifter 10 in the direction of the spindle axis AX0 and thenseparate the shifter bearing B3 from the side surface 12 a, 12 b of theoutward groove 12. It is therefore possible to keep the shifter bearingB3 separated from both the side surfaces 12 a and 12 b of the outwardgroove 12. The embodiment provides a lathe capable of elongating thelife of the shifter bearing.

(2) Configuration of the Lathe:

FIG. 1 schematically shows a configuration of the NC (numerical control)lathe 1 provided with the movable front spindle 42. FIG. 1 is only asimplified example for explanation and the invention is not limitedthereto. A positional relation between elements is only an example forexplanation. The left and right direction may be replaced by the up anddown direction or the front and back direction. The up and downdirection may be replaced by the left and right direction or the frontand back direction. The front and back direction may be replaced by theleft and right direction or the up and down direction. The rotationaldirection may be inversed. If something is the same as something indirection or position, they may be the same or almost the same within anerror range.

The lathe 1 may include the front headstock 41 provided with the frontspindle 42, a guide bush 35, the back headstock 51 provided with theback spindle 52, a gang tool post 31, a tool post for back machining 32,a turret tool post 33, all of which may be mounted on a base 2. Thefront spindle 42 may be an example of the main spindle. The frontheadstock 41 may be an example of the main headstock. The back spindle52 may be an example of the sub spindle. The back headstock 51 may be anexample of the sub headstock. The gang tool post 31, the tool post forback machining 32, and the turret tool post 33 may be collectivelyreferred to as the tool post 30. The lathe 1 may further include an NC(numerical control) apparatus 80 which controls movement of the frontheadstock 41, the back headstock 51, the guide bush 35, and the toolpost 30. The NC apparatus 80 may be arranged in a different positionfrom that shown in FIG. 1.

As shown in FIG. 1, the front headstock 41 provided with the frontspindle 42 may be movable in the Z-axis direction. The back headstock 51provided with the back spindle 52 may be movable in the Z-axis directionand in the X-axis direction. The gang tool post 31 may be movable in theX-axis direction and in the Y-axis direction. The tool post for backmachining 32 may be movable in the Y-axis direction. The turret toolpost 33 may be movable in the X-axis direction, in the Y-axis direction,and in the Z-axis direction. The Z-axis direction may be an example of adirection of the spindle axis. The Z-axis direction may be perpendicularto the X-axis direction. The Z-axis direction may be perpendicular tothe Y-axis direction. The X-axis direction may be perpendicular to theY-axis direction. The Z-axis direction and the X-axis direction maycross each other at any angle except right angles. The Z-axis directionand the Y-axis direction may cross each other at any angle except rightangles. The X-axis direction and the Y-axis direction may cross eachother at any angle except right angles. The direction of movement of thefront headstock 41, the back headstock 51, and the tool post 30 may notbe limited to those in FIG. 1.

The base 2 may be referred to as a bed or a table. The base 2 maydirectly or indirectly support the front headstock 41, the guide bush35, the back headstock 51, and the tool post 30. The guide bush 35 maybe supported by a guide bush support 36 on the base 2 as shown in FIG.1.

The front spindle 42 may be provided with a chuck such as a collet toreleasably hold a cylindrical (bar) workpiece W1 inserted in the Z-axisdirection. The NC apparatus 80 may rotate the front spindle 42 on aspindle axis AX1 extended in the longitudinal direction of the workpieceW1 by a driving unit such as a built-in motor. The front spindle 42 maythereby rotate the workpiece W1 on the spindle axis AX1. The guide bush35 provided in a position on the front side of the front spindle 42 mayslidably support the longitudinal workpiece W1 inserted in the frontspindle 42 in the Z-axis direction. The guide bush 35 may be rotatableon the spindle axis AX1 in synchronization with the front spindle 42.The technology may be applied to a lathe where no guide bush isprovided.

The back spindle 52 may receive the workpiece W1 whose front side hasbeen machined from the front spindle 42 opposite the back spindle 52.The back spindle 52 may be provided with the chuck 60 such as a colletto releasably hold the workpiece W0, whose front side has been machined,inserted in the Z-axis direction with the spindle axes AX1 and AX0 arealigned. The NC apparatus 80 may rotate the back spindle 52 on thespindle axis AX0 by a driving unit such as the built-in motor 55. Theback spindle 52 may thereby rotate the workpiece W0 on the spindle axisAX0. The back spindle 52 may be referred to as an opposite spindle sinceit is opposite the front spindle. The spindle axis AX1 of the frontspindle 42 and the spindle axis AX0 of the back spindle 52 may berollectively called the spindle axis AX0. The workpiece W1 held by thefront spindles 42 and the workpiece W0 held by the back spindle 52 maybe collectively called the workpiece W0.

The tool post 30 may have a plurality of tools T1 attached there. Thegang tool post 31 and the turret tool post 33 may be available inmachining the front side of the workpiece W1 supported by the guide bush35. The plurality of the tools T1 may include a cut-off tool for use tocut off the workpiece W0 held by both the front spindle 42 and the backspindle 52. The tool post for back machining 32 and the turret tool post33 may be available in machining the back side of the workpiece W0 cutoff with the cut-off tool .

The NC apparatus 80 may include a CPU (Central Processing Unit), a ROM(Read Only Memory) , a RAM (Random Access Memory), a timer circuit, andan I/F (Interface) to execute an NC program upon receipt of input via anot-shown operation panel or an external computer. The NC apparatus 80may control movement of the headstock 41, the headstock 51, and the toolpost 30 and further control rotation of the front spindle 42, the backspindle 52, and the guide bush 35. The NC program may be stored in theRAM by the operator via the operation panel 80 and the externalcomputer.

FIG. 2 is a vertical section view schematically showing the backheadstock 51 along the spindle axis AX0 including a block diagram of anactuator 69 in a distant position. The upper side with respect to thespindle axis AX0 shows the closed state in which a collet 61 is in theclosed state ST2 and a product ejector 70 is retracted toward the right.The lower side with respect to the spindle axis AX0 shows the openedstate in which the collet 61 is in the opened state ST1 and the productejector 70 is advanced toward the left. For convenience of explanation,the workpiece W0 as a product may be ejected toward the left (to thefront side D1) by the ejector 70 and the ejector is retracted to theright (to the rear side D2). The direction separating from the spindleaxis AX0 is an outward direction while the direction approaching thespindle axis AX0 is an inward direction. The front or forward side, therear or rearward side, the outer or outward side, and the inner orinward side each represents positional relationship. A positionrepresented by the front or forward side or the rear or rearward sidemay include a range of approximate positions in the Z-axis direction. Aposition represented by the outer or outward side and the inner orinward side may include a range of approximate positions in a directionperpendicular to the spindle axis AX0. FIG. 3 schematically shows anappearance of the chucking mechanism 6 a mounted outside the backspindle 52. FIG. 4 schematically shows a vertical section of thechucking mechanism 6 a mounted outside the back spindle 52. FIG. 5schematically shows an appearance of the claw 20 of the chuckingmechanism 6 a. FIG. 6 schematically shows an appearance of a claw holder26 holding the tilt claw 20. FIG. 7 schematically shows an appearance ofthe shifter 10 of the chucking mechanism 6 a. FIG. 8 schematically showsthe shifter drive unit DR1. FIG. 9 to FIG. 12 each schematically shows avertical section around the chucking mechanism 6 a. For ease ofunderstanding, the section view in FIG. 2 and FIG. 4 includesnon-hatched sections.

The back headstock 51 may be provided with the back spindle 52 havingthe collet 60 holding the workpiece W0 whose front side has beenmachined, the spindle support 53 supporting the back spindle 52, thebuilt-in motor 55 driving the back spindle 52, the chuck operatingapparatus 6 operating the chuck 60, and the product ejector 70 ejectingthe workpiece W0 as a product. The spindle support 53 may be integrallyformed with the back headstock 51 and may be a separate member mountedon the back headstock 51. The spindle support 53 may comprise a frontunit having the front bearing B1 and a rear unit having the rear bearingB2. The front unit may be integrally formed with the back headstock 51while the rear unit may be a separate member mounted on the backheadstock 51. The front unit may be a separate member mounted on theback headstock 51 while the rear unit may be integrally formed with theback headstock 51. The product ejector 70 may be replaced by a productpipe through which the workpiece W0 as a product is carried to the rightin FIG. 2

The back spindle 52 may be provided with a through-hole 52 a for passingthe product ejector 70 in the Z-axis direction. The back spindle 52 maybe rotatably mounted on the spindle support 53 by the rolling bearingsB1 and B2 to be driven by the built-in motor 55 to rotate on the spindleaxis AX0. A chuck sleeve 63 and a push sleeve 65 may be inserted intothe through-hole 52 a in the Z-axis direction. The chuck sleeve 63 andthe push sleeve 65 each may have a through-hole along the spindle axisAX1 where the product ejector 70 is inserted in the Z-axis direction.The sleeves 63 and 65 surrounding the product ejector 70 may rotate onthe spindle axis AX1 as the back spindle 52 is rotated.

The chuck 60 mounted at the front end of the back spindle 52 may includethe collet 61 and a cap 62. The collet 61 may have a tapered part 61 aon the outer circumference thereof. The tapered part 61 a may begradually thinner toward the rear. The tapered part 61 a may have a slitformed in a plurality of positions (three positions, for example). Thecap 62 may be attached at the front end of the back spindle 52 to holdthe collet 61. The collet 61 may hold the workpiece W0 when the taperedpart 61 a is pushed by an inverted tapered part 63 a of the chuck sleeve63. The collet 61 may release the workpiece W0 when the tapered part 61a is released from the inverted tapered part 63 a. The chuck 60 may havethe closed state ST2 holding the workpiece W0 and the opened state ST1releasing the workpiece W0. The collet 61 may rotate as the back spindleis rotated. The workpiece W0 released from the collet 61 may be ejectedto the left (in FIG. 2) as the product ejector 70 is advanced.

The front bearing B1 may be mounted in a position on the front side ofthe chucking mechanism 6 a. The rear bearing B2 may be mounted in aposition on the rear side of the built-in motor 55. The bearings B1 andB2 in FIG. 2 may be ball bearings, but they may be roller bearings andothers. The inner ring of the bearing may be mounted on the outercircumference of the back spindle 52. The outer ring of the bearing maybe mounted on the spindle support 53 .

As shown in FIG. 1, a plurality of structures such as the gang tool post31, the tool post 32 for back machining, and the turret tool post 33 mayexist in a direction from the back headstock 51 toward the guide bushsupport 36 of the guide bush 35. The back headstock 51 may have a bodypart 51 a movable in the X-axis and Z-axis directions with respect tothe base 2. The body part 51 a can approach the guide bush 35 only tothe extent that interference with the tool post 30 is avoided. The backspindle 52 may have an elongated front part to bring the front end closeto the guide bush 35. The back headstock 51 may have an elongated part51 b rotatably supporting the elongated front part of the back spindle52. The part 51 b may be elongated to the extent that interference withthe tool post 30 and other structures is avoided.

The built-in motor 55 may be mounted in a position on the rear side ofthe chucking mechanism 6 a between the front bearing B1 and the rearbearing B2. The built-in motor 55 may be provided with a stator 56 onthe side of the spindle support 53 and with a rotor 57 on the side ofthe back spindle 52 to rotate the back spindle 52 under timing controlof the NC apparatus 80. The back spindle 52 may be driven by an externalmotor with a belt. The expanding and shrinking belt causes a problemthat the rotations of the back spindle cannot exactly follow therotations of the motor. Further, repeated operations cause a wear orbreakage of the belt. Use of the built-in motor 55 eliminates theproblem and improves the rotation following capability of the backspindle 52.

The chuck operating apparatus 6 may include the chuck sleeve 63, acollet open spring 64, the push sleeve 65, the chucking mechanism 6 aincluding the claw 20 and the shifter 10, and the shifter drive unit DR1including the shifter lever 68 and the collet actuator 69. InEmbodiments 6 and 7 of the invention, the shifter 10 may be an exampleof one member and the claw 20 may be an example of the other member.

The chuck sleeve 63 having the inverted tapered part 63 a on the innercircumference of the front end thereof may be mounted outside the collet61 with respect to the spindle axis AX0. The inverted tapered part 63 amay become gradually separated from the spindle axis AX0 toward thefront as along the tapered part 61 a of the collet 61. The chuck sleeve63 may be slidable in the Z-axis direction. As the chuck sleeve 63slides toward the front, the tapered part 61 a of the collet 61 may betightened inwards (into the closed state ST2). As the chuck sleeve 63slides toward the rear, the tapered part 61 a of the collet 61 may beloosened (into the opened state ST1). The spring 64 may include a coilspring. The spring 64 may be hooked to the collet 61 at a front end andto the inner circumference of the chuck sleeve 63 at a rear end to applyrearward force to the chuck sleeve 63. The front end face of the pushsleeve 65 may be in contact with the rear end face of the chuck sleeve63. As shown in FIG. 4, a rear end face 65 b of the push sleeve 65 maybe in contact with a contact end 22 b of the claw 20. The push sleeve 65may be slidable in the Z-axis direction. The push sleeve 65 may movetoward the front when pushed by the claw 20 and move toward the rear byrearward force of the spring 64 when released from the claw 20.

The chucking mechanism 6 a may be mounted outside the back spindle 52and between the front bearing B1 and the rear bearing B2. The chuckingmechanism 6 a of the embodiment may be an inner-claw type that the claw20 is mounted inside the shifter 10 with respect to the spindle axisAX0. The chucking mechanism 6 a may be mounted in a position on thefront side of the built-in motor 55 with respect to the Z-axisdirection.

The claw 20 of the chucking mechanism 6 a may be mounted outside theback spindle 52 with respect to the spindle axis AX0 and between thefront bearing B1 and the rear bearing B2 to be rotatable on the spindleaxis AX0. As shown in FIG. 4, the chucking mechanism 6 a may include theclaws 20 in opposite positions with respect to the spindle axis AX0. Thefront end of the claw 20 may be a root 22 whose distance from thespindle axis AX0 is substantially constant. The rear end of the claw 20may be the movable end 21 whose distance from the spindle axis AX0varies. As shown in FIG. 5, a recess 20 a may be formed on the outersurface of the claw 20 with respect to the spindle axis AX0. The recess20 a may be dented toward the spindle axis AX0 between the root 22 andthe movable end 21. The shifter 10 may be mounted outside the claw 20 ina position corresponding to the recess 20 a.

The roof 22 may have a through-hole 22 a and the contact end 22 b. Aclaw pin 23 may be inserted into the through-hole 22 a in the directionof the tilt axis as shown in FIG. 3 and FIG. 4. The contact end 22 b maybe in contact with the rear end face 65 b of the push sleeve 65. Theclaw 20 may tilt on the claw pin 23 inserted into the through-hole 22 a.The contact end 22 b may be closer to the spindle axis AX0 than the hole22 a is. The contact end 22 b may be pushed toward the rear by the rearend face 6 b of the push sleeve 65. The contact end 22 b may push therear end face 6 b of the push sleeve 65 toward the front.

The movable end 21 of the claw 20 may vary in distance from the spindleaxis AX0 according to operation of the claw 20. As shown in the lowerhalf of FIG. 2 with respect to the spindle axis AX0, when the contactend 22 b of the claw 20 is pushed toward the rear by the push sleeve 65,the movable end 21 may be brought into the first posture PO1 in whichthe movable end 21 is comparatively distant from the spindle axis AX0 tothereby bring the collet 61 into the opened state ST1. As shown in theupper half of FIG. 2 with respect to the spindle axis AX0, when thecontact end 22 b of the claw 20 pushes the push sleeve 65 toward thefront, the movable end 21 may be brought into the second posture PO2 inwhich the movable end 21 is comparatively close to the spindle axis AX0to thereby bring the collet 61 into the closed state ST2. The claw 20may have the first posuture PO1 in which the movable end 21 iscomparatively distant from the spindle axis AX0 to thereby bring thecollet 61 into the opened state ST1 and the second posture PO2 in whichthe movable end 21 is comparatively close to the spindle axis AX0 tothereby bring the collet 61 into the closed state ST2.

The recess 20 a of the claw 20 may have the groove 25 formed near themovable end 21. The roller 15 of the shifter 10 may fit in the groove 25when the movable end 21 is comparatively distant from the spindle axisAX0 (when the claw 20 is in the first posture PO1 to bring the collet 61into the opened state ST1). The direction of the groove 25 may beperpendicular to the spindle axis AX0. The roller 15 of the shifter 10may roll on the outer side surface of the claw 20 with respect to thespindle axis AX0 from the groove 25 to the movable end 21. The outerside surface of the movable end 21 may be outside the outer side surfaceof the recess part 20 a with respect to the spindle axis AX0. The claw20 may tilt around the through-hole 22 a of the root 22. When thecontact position of the roller 15 with the claw 20 is changed from thegroove 25 to the movable end 21, the movable end 21 may be brought closeto the spindle axis AX0 to thereby bring the collet 61 into the closedstate ST2.

The chucking mechanism 6 a may further include the claw holder 26mounted outside the back spindle 52 as shown in FIG. 6. The claw holder26 may have a larger diameter portion 26 a at the front side thereof anda thinner diameter portion 26 b extended from the larger diameterportion 26 a to the rear end thereof. The claw holder 26 may have athrough-hole 26 c continuing from the larger diameter portion 26 a tothe thinner diameter portion 26 b. The back spindle 52 may be insertedinto the through-hole 26 c in the Z-axis direction. The thinner diameterportion 26 b may have a slit 26 d in a position corresponding to theclaw 20. The shifter 10 may be slidably mounted outside the thinnerdiameter portion 26 b with respect to the spindle axis AX0. The outercircumference 26 e of the thinner diameter portion 26 b may act as aguide surface for the shifter 10 sliding in the Z-axis direction. Thelarger diameter portion 26 a may be provided with a claw pin hold 27 forremovably holding the claw pin 23 whose longitudinal direction may bealong the tilt axis of the claw 20. The claw pin hold 27 may be devidedby a gap 27 a receiving the root 22 of the claw 20. The larger diameterportion 26 a may have a recess 27 b adjacent to the hold 27 each. Thehold 27 each may be a part between the gap 27 a and the recess 27 b. Thehold 27 each may have a through-hole 27 c provided through the recess 27b and the gap 27 a. The claw pin 23 may be removably inserted in thethrough-hole 27 c.

Attaching the claw 20 to the claw holder 26 is being described. First,the root 22 of the claw 20 may be put in the gap 27 a of the claw pinhold 27. The claw pin 23 may be inserted in the through-hole 27 c of thehold 27 each and the through-hole 22 a of the root 22. Then a stop sing24 may be attached to both ends of the claw pin (FIG. 3). The clawholder 26 having the claw 20 may be rotated on the spindle axis AX0.

The shifter 10 of the chucking mechanism 6 a may be movable in theZ-axis direction and rotatable on the spindle axis AX0 in a positionoutside the recess 20 a of the claw 20 and the thinner diameter portion26 b of the claw holder 26 with respect to the spindle axis AX0. Theshifter 10 may slide in the Z-axis direction within a range of the claw20 disposed between the front bearing B1 and the rear bearing B2. Theshifter 10 may be brought in the first position LO1 to bring the claw 20into the first posture PO1 and in the second position LO2 to bring theclaw 20 into the second posture PO2. The shifter 10 may entirely overlapthe claw 20 in the Z-axis direction. The embodiment provides a shorterchucking mechanism in the Z-axis direction compared to the chuckingmechanism of outer-claw type. The embodiment further provides alightweight chucking mechanism by eliminating the need of the extendedheavier portion 22 c as provided in the outer-claw type (FIG. 13, 14)

The shifter 10 may have a through-hole 10 a for receiving the clawholder 26 in the Z-axis direction (FIG.7). The shifter 10 may have theoutward groove 12 entirely formed around the outer surface 11 thereofwith respect to the spindle axis AX0 to receive the insertion part 68 aof the shifter lever 68 (FIG. 8). The outward groove 12 may have thefront side surface 12 a and the rear side surface 12 b opposite to eachother in the Z-axis direction (FIG. 3, 8) and further have a bottomsurface 12 c between the front side surface 12 a and the rear sidesurface 12 b. The bottom surface 12 c may have a recess 12 d steppeddown toward the spindle axis AX0 to receive the fixed part of the innerring of the shifter bearing B3 as shown in FIG. 9 to FIG. 12.

The roller 15 rolling in the Z-axis direction may be mounted on the rearend of the shifter 10 in the contact position with the claw 20 as shownin FIG. 2 to FIG. 4. The roller 15 may have the insertion hole 15 a forreceiving the roller pin 16 along the direction of the rolling axis AX3.The roller 15 may roll jyouon the roller pin 16 passed in the insertionhole 15 a. The shifter 10 may be provided with the hold 14 removablyhaving the roller pin 16 in a position on the rear side of the outwardgroove 12. As shown in FIG. 3 and FIG. 7, the hold 14 may be devided bya gap 14 a receiving the roller 15. The shifter 10 may have a recess 14b adjacent to the hold 14 each. The hold 14 each may be a part betweenthe gap 14 a and the recess 14 b. The hold 14 each may have an insertionhole 14 c provided through the recess 14 b and the gap 14 a. The rollerpin 16 may be removably passed in the insertion hole 14 c.

Attaching the roller 15 to the shifter 10 is being described. First, theroller 15 may be put in the gap 14 a of the hold 14. The roller pin 16may be passed in the insertion hole 14c of the hold 14 each and theinsertion hole 15 a of the roller 15. Then a stop sing 17 may beattached to both the ends of the roller pin 16. The roller 15 may bethereby attached to the shifter 10 operably on the rolling axis AX3. Inremoving the roller 15 from the shifter 10, the stop ring 17 may beremoved to pull the roller pin 16 out from the insertion hole 15 a.

The shifter drive unit DR1 may include the shifter lever 68 providedwith the shifter bearing B3 and the collet actuator 69 as shown in FIG.2 and FIG. 8. The shifter drive unit DR1 may have the shifter lever 68in opposite positions with respect to the spindle axis AX0 as shown inFIG. 9 to FIG. 12. The shifter lever 68 each may have a base end 68 b, adistal end 68 c, and a pivot 68 d. The insertion part 68 a of theshifter lever 68 may be provided on an opposite surface near the distalend 68 c to be received by the outward groove 12 of the shifter 10. Whenthe base end 68 b is driven by the actuator 69, the shifter lever 68 mayturn about the pivot 68 d to move the distal end 68 c a littleapproximately in the Z-axis direction, and thereby move the shifter 10in the Z-axis direction. The shifter 10 may rotate on the spindle axisAX0. The shifter lever 68, however, may not rotate on the spindle axisAX0. The insertion part 68 a of the shifter lever 68 may be thereforeprovided with the shifter bearing B3 capable of being brought intocontact with the side surface 12 a, 12 b of the outward groove 12 asshown in FIG. 9 to FIG. 12. The outer ring of the shifter bearing B3 maybe rotatable on a rotation axis AX4 perpendicular to the spindle axisAX0 to be possibly in contact with the side surface 12 a, 12 b of theoutward groove 12. The shifter lever 68 may be brought in such aposition as to keep the outer ring of the shifter bearing B3 separatedfrom both the front side surface 12 a and the rear side surface 12 b.Accordingly, the outer ring of the shifter bearing B3 may be allowed totouch only one of the front side surface 12 a and the rear side surface12 b of the outward groove 12.

The actuator 69 may include a cylinder 69 a and a piston 69 b protrudingfrom the cylinder 69 a to be rotatably connected to the base end 68 b ofthe shifter lever 68. The actuator 69 may drive the shifter lever 68under control of the NC apparatus 80. The actuator 69 may be anelectronic actuator having a electronic cylinder. An air cylinder and ahydraulic cylinder may be used instead.

The shifter bearing may include a rolling bearing whose inner ringrotatable with respect to the spindle axis may fit in the groove to bebrought into contact with the shifter. Such shifter may be referred toas a coaxial shifter bearing. The coaxial shifter bearing may be mountedoutside the shifter with respect to the spindle axis and thereforelarger in diameter. In the embodiment, the outer ring may be rotatableon the rotation axis AX4 perpendicular to the spindle axis AX0. Suchshifter bearing may be referred to as an opposite shifter bearing. Theopposite shifter bearing may be smaller than the coaxial shifer bearingand also less expensive. If, however, such smaller shifter bearing iskept in contact with the side surface 12 a, 12 b of the outward groove12 of the shifter 10, the shifter bearing B3 likely wears due toproduced heat since it rotates faster than the back spindle 52 rotatingon the spindle axis AX0.

In the embodiment, the shifter drive unit DR1 may drive the shifterlever 68 to separate the shifter bearing B3 from the side surface 12 a,12 b of the outward groove 12 after moving the shifter 10 in the Z-axisdirection. The shifter drive unit DR1 may be driven by the actuator 69under control of the NC apparatus 80. The shifter drive unit DR1 mayinclude the NC apparatus 80. The operation of the shifter drive unit DR1is being explained referring to FIG. 2 and FIG. 8 to FIG. 12.

As shown in FIG. 9, the shifter 10 may be brought in the first positionLO1 on the front side to bring the claw 20 into the first posture PO1with the movable end 21 away from the spindle axis AX0. The collet 61may be brought into the opened state ST1 (FIG. 2) and the shifterbearing B3 may be separated from both the side surfaces 12 a and 12 b(FIG. 8) of the outward groove 12 of the shifter 10. Tightening thecollet 61 to hold the workpiece W0 is being explained. The NC apparatus80 may drive the shifter lever 68 to advance the piston 69 b protrudingfrom the cylinder 69 a toward the front and thereby bring the insertionpart 68 a toward the rear. The outer ring of the shifter bearing B3 maybe brought into contact with the rear side surface 12 b to move theshifter 10 to the second position LO2 on the rear side as shown in FIG.10. As the result, the roller 15 of the shifter 10 may roll on therolling axis AX3 from the groove 25 to the movable end 21 to bring theclaw 20 into the second posture PO2 with the movable end 21 close to thespindle axis AX0. The contact end 22 b of the claw 20 may push the chucksleeve 63 toward the front by the push sleeve 65 (FIG. 2). The invertedtapered part 63 a of the chuck sleeve 63 may push the tapered part 61 aof the collet 61 toward the spindle axis AX0. The collet 61 may bethereby brought into the closed state ST2.

The NC apparatus 80 may then drive the shifter lever 68 by the actuator69 to separate the shifter bearing B3 from the rear side surface 12 b tothe extent not to touch the front side surface 12 a. The piston 69 bprotruding from the cylinder 69 a may move a little bit to the rear andthe distal end 68 c of the shifter lever 68 may thereby move a littlebit to the front. As the result, the shifter bearing B3 may be separatedfrom both the side surfaces 12 a and 12 b of the outward groove 12 whilethe shifter 10 stays in the second position LO2 as shown in FIG. 11. Theshifter bearing B3 is not rotated even if the shifter 10 rotates at highspeed on the spindle axis AX0.

Opening the collet 61 to release the workpiece W0 is being explained.The NC apparatus 80 may drive the shifter lever 68 to retract the piston69 b protruding from the cylinder 69 a toward the rear and thereby bringthe insertion part 68 a toward the front. The outer ring of the shifterbearing B3 may be brought into contact with the front side surface 12 ato move the shifter 10 to the first position LO1 on the front side asshown in FIG. 12. As the result, the roller 15 of the shifter 10 mayroll on the rolling axis AX3 from the movable end 21 to the groove 25.The collet open spring 64 may push the push sleeve 65 toward the rear bythe chuck sleeve 63 (FIG. 2) to bring the claw 20 into the first posturePO1 with the movable end 21 away from the spindle axis AX0. The invertedtapered part 63 a of the chuck sleeve 63 pushing the tapered part 61 aof the collet 61 toward the spindle axis AX0 may be retracted. Thecollet 61 may be thereby brought into the opened state ST1.

The NC apparatus 80 may then drive the shifter lever 68 by the actuator69 to separate the shifter bearing B3 from the front side surface 12 ato the extent not to touch the rear side surface 12 b. The piston 69 bprotruding from the cylinder 69 a may move a little bit to the front andthe distal end 68 c of the shifter lever 68 may thereby move a littlebit to the rear. As the result, the shifter bearing B3 may be separatedfrom both the side surfaces 12 a and 12 b of the outward groove 12 whilethe shifter 10 stays in the first position LO1 as shown in FIG. 9. Theshifter bearing B3 is not rotated even if the shifter 10 rotates at highspeed on the spindle axis AX0.

As described above, the opposite shifter bearing B3 may touch the frontside surface 12 a or the rear side surface 12 b of the outward groove 12only when the collet 61 is switched between the opened state ST1 and theclosed state ST2. The opposite shifter bearing B3 in this embodiment canreduce the number of rotations compared to the coaxial shifter bearingB3 rotating following the rotation of the shifter on the spindle axis.Reduced rotations prevent occurance of heat and thereby suppress wear ofthe shifter bearing B3. The embodiment provides a lathe capable ofelongating the life of the shifter bearing that is small andinexpensive.

(3) Effect of the Embodiment:

As shown in FIG. 1, a plurality of the structures including the toolpost 30 may exist in a forward area of the back headstock 51. The bodypart 51 a (FIG. 2) of the back headstock 51 can approach the guide bush35 only to the extent that interference with the structures is avoided.The back spindle 52 may have the elongated front part to be supported bythe elongated part 51 b of the back headstock 51. That would increase aninner space of the elongated part 51 b in the Z-axis direction. It is,however, difficult to simply dispose the chucking mechanism 6 b (FIG.13, FIG. 14) between the front bearing and the back bearing where thebuilt-in motor is mounted. An additional intermediate bearing would berequired to rotatably support the high speed rotation spindle since thechucking mechanism 6 b (outer-claw type) is longitudinal in the spindleaxis direction. Such arrangement would make the headstock structurecomplicated and elongate the front part of the spindle too long.Further, the chucking mechanism disposed in a position on the rear sideof the rear bearing would be disadvantageous to high speed rotations ofthe spindle.

In the chucking mechanism 6 a as shown in FIG. 2 to FIG. 4 and FIG. 9 toFIG. 12, the claw 20 may be mounted outside the back spindle 52 and theshifter 10 may be mounted outside the claw 20 movably in the Z-axisdirection. The chucking mechanism 6 a of inner-claw type is shorter thanthe chucking mechanism 6 b of outer-claw type in the Z-axis direction.The shorter chucking mechanism 6 a may be mounted between the frontbearing B1 and the rear bearing B2 where the built-in motor is mountedwithout a need of the additional intermediate bearing to ensure highspeed rotations of the back spindle 52. The chucking mechanism 6 a maybe mounted in an inner space of the elongated front part of the backheadstock 51 adapted to the elongated front part of the back spindle 52.Such arrangement could shorten the rear part of the back spindle 52instead. The chucking mechanism 6 a may be smaller in diameter than thebuilt-in motor 55. The chucking mechanism 6 a may be therefore suitablefor the space of the elongated front part of the back headstock 51 toavoid interference with the structures. The embodiment as describedabove shortens the back spindle 52 in the Z-axis direction and furthersimplifies the chuck operating apparatus 6 since the chucking mechanism6 a is closer to the collet 61 mounted at the front end of the backspindle 52.

The roller 15 may be attached to the shifter 10 in the contact positionwith the claw 20. The roller 15 may roll in the spindle axis directionas the chuck 60 is operated. The friction of the shifter 10 against theclaw 20 is reduced and the load on the actuator 69 is thereby reduced.The roller 15 and the claw 20 touching each other gradually wear butwear amount is reduced. The embodiment facilitates parts replacementsince replacement of the roller 15 does not require a time-consumingreplacement of the whole shifter 10 mounted entirely around the backspindle 52. Replacement of the roller 15 is easier for the operator. Theoperator can take the roller 15 out of the shifter 10 outward in thediameter direction perpendicular to the spindle axis AX0 only byremoving the roller pin 16 from the hold 14. The operator can attach theroller 15 to the shifter 10 only by mounting the pin 16 passed in thehole 15 a to the hold 14. Replacement of the claw 20 is easier since theclaw 20 is not mounted entirely around the back spindle 52. Theembodiment provides a lathe capable of facilitating maintenance of thechucking mechanism.

To suppress wear of the shifter bearing B3 of opposite-type, it may benecessary to keep the shifter bearing B3 separated from both the sidesurfaces 12 a and 12 b of the outward groove 12 of the shifter 10 aftermoving the shifter 10 in the Z-axis direction. As shown in FIG. 11, theroller 15 of the shifter 10 brought in the second position LO2 on therear side may push the movable end 21 of the claw 20 toward the spindleaxis AX0 to bring the collet 61 into the closed state ST2 to hold theworkpiece W0. The roller 15 receives strong force from the movable end21 to prevent the shifter 10 from moving in the Z-axis direction withthe shifter bearing B3 kept separated from both the side surfaces 12 aand 12 b of the outward groove 12. As shown in FIG. 9, the roller 15 ofthe shifter 10 brought in the first position LO1 on the front side mayfit in the groove 25 of the claw 20 to bring the collet 61 into theopened state ST1 to release the workpiece W0 with the shifter bearing B3kept separated from both the side surfaces 12 a and 12 b of the outwardgroove 12. Without the groove 25, the roller 15 would receive littleforce from the collet open spring 64 to allow the shifter 10 to move inthe Z-axis direction. The shifter bearing B3 would thereby undesirablybrought into contact with the side surface 12 a, 12 b. The embodimentprovides a lathe capable of elongating the life of the shifter bearing.

(4) Modifications:

The invention may be embodied in various modifications. The lathe may bea lathe of slidable-spindle type and instead a lathe ofstationary-spindle type. The spindle may be the sub spindle and insteadthe main spindle. The number of claws may be two and instead three ormore.

The shifter bearing may be the shifter bearing of coaxial type and theclaw 20 may not be provided with the groove 25 in Embodiments 1 to 5.The shifter 10 may not be provided with the roller 15 in Embodiments 1to 3. The roller may be attached to the claw in the contact positionwith the shifter to roll in the Z-axis direction in Embodiments 1 to 3,6 and 7. The chucking mechanism may be mounted in a position on the rearside of the rear bearing B2 or may be replaced by the chucking mechanismof outer-claw type in Embodiments 4 to 7.

FIG. 13 and FIG. 14 each representing an example included in Embodiments4 to 7 of the invention shows a vertical section view around thechucking mechanism 6 b of outer-claw type disposed in a position on therear side of the rear bearing B2 (not shown). In FIG. 13, the shifter 10may be brought in the second position LO2 on the rear side to bring theclaw 20 into the second posture PO2. The collet 61 (not shown) may bebrought into the closed state ST2. In FIG. 14, the shifter 10 may bebrought in the first position LO1 on the front side to bring the claw 20into the first posture PO1. The collet 61 (not shown) may be broughtinto the opened state ST1.

The shifter 10 (FIG. 13, 14) may be of a shape surrounding the backspindle 52 on the spindle axis AX0 and in contact with a plurality ofthe claws 20. The roller 15 may be removaly mounted on the shifter 10 ina contact position with the claw 20 on the rear side of the outwardgroove 12 receiving the shifter bearing B3. The roller 15 may roll inthe Z-axis direction. The claw 20 may have the movable end 21 protrudingforwards and the extended portion 22 c elongated rearwards on the rearside of the claw pin 23. The claw 20 may tilt in the direction that thedistance between the movable end 21 and the spindle axis AX0 varies. Theclaw 20 may have the groove 25 formed near the movable end 21 to receivethe roller 15 when the collet 61 is in the opened state ST1.

The collet 61 in the closed state ST2 (FIG. 13) is being opened in amanner as described below. The shifter lever 68 may be driven to movethe shifter bearing B3 forwards to thereby push the shifter 10 forwards.The roller 15 of the shifter 10 may roll on the rolling axis AX3 towardthe movable end 21 until it reaches the groove 25. The collet openspring 64 may push the push sleeve 65 rearwards by the chuck sleeve 63(FIG. 2). The movable end 21 may thereby approach the spindle axis AX0to bring the claw 20 into the first posture PO1. The chuck sleeve 63moves rearwards to release the collet 61 into the opened state ST1 (FIG.14).

The shifter lever 68 may be then driven to separate the shifter bearingB3 from the side surface of the outward groove of the shifter 10. Theshifter bearing B3 can be kept separated from both the side surfaces ofthe outward groove since the roller 15 of the shifter 10 fits in thegroove 25 of the claw 20. The shifter bearing B3 therefore does notrotate at high speed even if the shifter 10 rotates at high speed on thespindle axis AX0, which elongates the life of the shifter bearing B3.

FIG. 15 and FIG. 16 each representing an example included in Embodiments1 to 3, 6 and 7 of the invention shows a vertical section view around achucking mechanism 6 c of inner-claw type disposed between the bearingsB1 and B2 (not shown). In FIG. 15, the shifter 10 may be brought in thesecond position LO2 on the rear side to bring the claw 20 into thesecond posture PO2. The collet 61 (not shown) may be brought into theclosed state ST2. In FIG. 16, the shifter 10 may be brought in the firstposition LO1 on the front side to bring the claw 20 into the firstposture PO1. The collet 61 (not shown) may be brought into the openedstate ST1. In Embodiments 6 and 7, the claw may be an example of one ofthe members and the shifter may be an example of the other.

The roller 15 may be removaly mounted on the claw 20 in a contactposition with the shifter 10 near the movable end 21. The roller 15 mayroll in the Z-axis direction. The shifter 10 may have the groove 25formed in a position on the rear side of the outward groove receivingthe shifter bearing B3 to receive the roller 15 when the collet 61 is inthe opened state ST1.

The collet 61 in the closed state ST2 (FIG. 15) is being opened in amanner as described below. The shifter lever 68 may be driven to movethe shifter bearing B3 forwards to thereby push the shifter 10 forwards.The roller 15 of the claw 20 may roll on the rolling axis AX3 toward therear end of the shifter 10 until it reaches the groove 25. The colletopen spring 64 may push the push sleeve 65 rearwards by the chuck sleeve63 (FIG. 2). The movable end 21 may thereby move away from the spindleaxis AX0 to bring the claw 20 into the first posture PO1. The chucksleeve 63 moves rearwards to release the collet 61 into the opened stateST1 (FIG. 16).

The shifter lever 68 may be then driven to separate the shifter bearingB3 from the side surface of the outward groove of the shifter 10. Theshifter bearing B3 can be kept separated from both the side surfaces ofthe outward groove since the roller 15 of the claw 20 fits in the groove25 of the claw 20. The shifter bearing B3 therefore does not rotate athigh speed even if the shifter 10 rotates at high speed on the spindleaxis AX0, which elongates the life of the shifter bearing B3.

(5) Conclusion:

As described above, the invention provides a lathe capable of shorteningthe spindle with respect to the spindle axis direction, a lathe capableof facilitating maintenance of the chucking mechanism, and a lathecapable of elongating the life of the shifter mechanism. The essentialoperations and effects of the invention may be available even from onlythe elements of independent claim. The elements disclosed in theembodiments may be mutually replaced or the combination thereof may bechanged. The disclosed elements may be mutually replaced by prioir artof the combination thereof may be changed. Such replacement and changemay be within the scope of the invention.

What is claimed is:
 1. A lathe comprising: a spindle rotatable on aspindle axis and provided with a chuck having a closed state to hold aworkpiece and an opened state to release the workpiece; and a chuckoperating apparatus which opens and closes the chuck, comprising: a tiltclaw provided outside the spindle and rotatable on the spindle axis, theclaw having a first posture to bring the chuck into the opened state anda second posture to bring the chuck into the closed state; a shifterprovided outside the spindle and rotatable on the spindle axis, theshifter being movable in a direction of the spindle axis to be broughtin a first position to bring the claw into the first posture and in asecond position to bring the claw into the second posture; and a drivingunit having a shifter lever which moves the shifter in the direction ofthe spindle axis, wherein an outward groove is entirely formed around anouter surface of the shifter with respect to the spindle axis to receivean insertion part of the shifter lever, the insertion part of theshifter lever has a shifter bearing capable of being brought intocontact with a side surface of the outward groove, and a roller isprovided on one of the claw and the shifter in a contact position withthe other to roll in the direction of the spindle axis and a groove isformed on the other to receive the roller when the chuck is in theopened state.